The protection of construction materials from the corrosive effects of chemicals in the environment has always received a great deal of attention from not only the designers of buildings, dams, piers, hydraulic systems, and storage vessels but also from the owners who want low maintenance structures and systems that remain in operating condition for long periods of time. Coatings, liners, paints, and various surface treatments have all been employed with varying degrees of success, and any chipping, cracking, pinholes, or delamination in the coatings or liners usually leads to rapid deterioration of the underlying surface.
Perhaps the most widely used construction material today, other than wood, is concrete and this is in part due to its cost, formability, and its resistance to adverse conditions. Among the adverse conditions which give the most challenge to designers of concrete structures are those conditions encountered in the handling of waste water and sewerage.
While concrete is widely used in waste water collection and treatment facilities, it is subject to significant corrosive attack when exposed, unprotected, to sulfide generation in waste water. Sources of sulfides in waste water include unregulated industrial discharges, degradation of sulfur-containing organic material, and the microbiological reduction of other forms of sulfur. Urban development and the construction of regional collection and treatment centers has increased waste water travel time in collection systems which consequently increases the opportunity for sulfide generation.
Hydrogen sulfide is a major portion of the odor associated with manholes and waste treatment facilities and it is toxic and corrosive. For concrete, the corrosion process begins with the oxidation of hydrogen sulfide to sulfuric acid. The acid subsequently reacts with the limestone based cement binder in the concrete thus weakening the surface structure leading to the deterioration of manholes, lift stations, and other exposed concrete surfaces.
In the past, a number of solutions to the problem of concrete corrosion have been sought. One early attempt employed vitrified clay liners, but these proved unsatisfactory. More recently, many epoxy coatings have been tested but these tend to fail wherever exposure to significant sulfuric acid attack occurs. Perhaps the most satisfactory protective system developed so far has been the application of pre-formed polyvinyl chloride (PVC) liners to concrete surfaces during construction. While this solution may hold promise for some new concrete construction, there are drawbacks such as handling and properly aligning the PVC sections, sealing the seams, the cost of sufficiently rigid and large diameter PVC structures, and the lack of a water-tight bond between the PVC liner and the underlying concrete which provides space for moisture and condensation to collect.
Furthermore, there is yet to be found any clear cut satisfactory method or materials for rehabilitating existing corroded concrete surfaces, particularly manholes. The current practice of coring out a manhole, inserting a PVC liner, and filling the resulting cavity between the liner and cored out wall with concrete grout has not proven to be a satisfactory solution as the grout tends to crack, become filled with moisture, and allow movement of the liner, requiring additional costly repair.
Another problem in rehabilitation efforts is that these projects do not readily allow for down time, so that conventional concrete surface repair using cement cannot easily take place. Thus, one object of the present invention is to devise a coating that bonds to concrete even while wet and provides protection from sulfuric and other acids.
While bonding coatings and liners have been used in the past, one of the problems is applying the coating so there are no cracks or pinholes. It is through these pinholes that acid can penetrate into the underlying concrete surface. Thus, it is another object of the present invention to provide a concrete liner which is resistant to pinhole and crack formation.
In a report entitled "Evaluation of Protective Coatings for Concrete" by John A Redner, et.al. of the County Sanitation District of Los Angeles County, Wittier, Calif. dated February 1995, it is concluded that: "To survive, the coating not only has to be acid proof and able to bond to the concrete substrate, but it also has to be applicator friendly." Therefore, it is still another object of the present invention to provide a composition which can be readily and successfully applied to concrete surfaces under varying conditions and with a high rate of success.
In the above report by Redner, et.al., the known concrete coatings were placed in the following categories: coal tar, coal tar mortar, concrete sealer, epoxy, epoxy mortar, liner, phenolic, polyester, polyester mortar, polyurea, silicone, specialty concrete, urethane, vinyl ester, and vinyl ester mortar. None of these proved satisfactory in all aspects.
It is, thus, yet another object of the present invention to provide for the application of polyester resin blended in a unique manner not previously employed and to achieve a degree of success not previously available with polymeric resins.
It is still another object of the present invention to provide a concrete liner which can be applied to a concrete surface having an acidic or basic surface, i.e. a pH which is either greater or less than 7.
One further object of the present invention is to provide a binder matrix into which aggregate or reinforcing material can be added in order to form molded, extruded, or cast articles which are substitutes for conventional concrete.
The foregoing and other objects are achieved by the present invention which is described below.